Wellhead seals of the prior art have involved the use of wedging action to spread sealing lips into sealing engagement with the interior of a wellhead housing and the exterior of a hanger, with a lip open to the pressure on its interior but not on its exterior or sealing side so that the pressure assists in urging the lip into a tight metal to metal sealing engagement. Other methods of energizing the seals have been employed to provide a radial force on the seal to urge it into tight sealing engagement with the cylindrical surface against which it is to seal.
An example of a seal with both wedging and an open lip exposed to pressure is disclosed in the U.S. Pat. No. 2,746,486 to J. L. Gratzmuller.
U.S. Pat. No. 2,405,152 to W. Kilchenmann discloses a resilient metal lip seal that is used to seal between eccentric tubular members.
U.S. Pat. No. 4,595,053 discloses an annular seal in which the seal is cup-shaped in section and is provided with an annular wedge which is received within the opening in the cup seal to force the lips of the cup seal outward and inward into tight sealing engagement with the interior of the housing and the exterior of the hanger. The sealing surfaces of the housing and hanger are provided with wickers which provide a series of threads for sealing.